Novel thermistor and method of making

ABSTRACT

This patent describes a thermistor comprising a plastic body member of a generally cylindrical configuration having an opening passing longitudinally therethrough, a plurality of threads on the exterior of said body in proximity to one end thereof, a thin metal film within the grooves but not on the lands of said threads and metal disposed on the exterior and interior of said body to establish a continuous metal path from the exterior of the end opposite said end having threads to the interior of said end opposite said end having threads, said metal path being composed of an electrically conductive metal having a hightemperature coefficient of resistivity.

United States Patent Continuation-impart of application Ser. No. 790,307, Jan. 10, 1969. This application Feb. 19, 1969, Ser. No. 800,610

NOVEL THERMISTOR AND METHOD OF MAKING 5 Claims, 5 Drawing Figs.

u.s.c|... 338/23,

338/300. 29/612, 29/620 lnt.Cl Hole 1/04 Field arse-rend 338/25,28,

[56] Relerences Cited UNITED STATES PATENTS 2,349,6l4 5/1944 Denisolfet al 338/28 E X 3,414,864 12/1968 Barrington 338/300 Primary Examiner--Rodney D. Bennett, Jr. Assistant Examiner-R. Kinberg Attorney-Pinkelstein & Mueth ABSTRACT: This patent describes a thermistor comprising a plastic body member of a generally cylindrical configuration having an opening passing longitudinally therethrough, a plurality of threads on the exterior of said body in proximity to one end thereof, a thin metal film within the grooves but not on the lands of said threads and metal disposed on the exterior and interior of said body to establish a continuous metal path from the exterior of the end opposite said end having threads to the interior of said end opposite said end having threads, said metal path being composed of an electrically conductive metal having a high-temperature coefficient of resistivity.

PATENTED m 19H Fla. 2

NOVEL TIIERMISTOR AND METHOD OF MAKING BACKGROUND OF THE INVENTION Various temperature measuring devices have been used including mercury thermometers, thermocouples, bimetallic strips, and the like. Most of these devicesmust be constructed of fragile glass and/or expensive metal components. The

known devices which are made of sturdy inexpensive materi- SUMMARY OF THE INVENTION Briefly, the present invention comprises a thermistor comprising a plastic body member of a generally cylindrical configuration having an opening passing longitudinally therethrough, a plurality of threads on the exterior of said body in proximity to one end thereof, a thin metal film within the grooves but not on the lands of said threads and metal disposed on the exterior andinterior of said body to establish a continuous metal path from the exterior of the end opposite said end having threads to the interior of said end opposite said end having threads, said metal path being composed of an electrically conductive metal having a high temperature coefficient of resistivity.

The invention also comprises the method of making a thermistor which comprises molding a plastic body member having a generally cylindrical configuration having an opening passing longitudinally therethro ugh and a plurality of threads on the exterior of said body in proximity to one end thereof, coating the inside and outside surface of said body with a thin electrically conductive metal film having a high temperature coefficient of restitivity, and removing said film from the lands of said threads but not the grooves of said threads to establish a continuous metal pathfrom the exterior of the end opposite said end having'threads to the interior of said end opposit said end having threads.

It is an object of the present invention to provide a novel,

DESCRIPTION OFPREFERRED EMBODIMENTS Turning to the drawings FIG. 1 is a plan view of a mold used to form the body of the thermistor;

FIG. 2 shows the application of the conductive metal coating to several thermistor bodies in an electroless plating bath;

FIG. 3 shows a side view with portions broken away of a thermistor body after it has been metal coated; FIG. 4 shows the coated thermistor body of FIG. 3 after some of the metal has been buffed from parts of the exterior of the body; and

FIG, 5 is a sectional view taken along the line 5-5 of FIG. 4.

Turning to the drawings in greater detail, the thermistor body may be formed, for example in a mold such as 12. Thermistor body 10 is then placed in a plating bath 14 where a metal coating I6 is applied to both the exterior and longitudinal interior opening 18. By the use of a buffer or grinder, metal is removed from the lands 20 of threads 22 leaving a metal path 24 within the grooves. The vertical metal path 26 and upper horizontal metal ring 28, as well as the metal on the interior of the body, are intended to be electrically connected to a power source.

The final body may be coated with a protective coating such as conformal coating 30. It is to be understood that the body of the thermistor is preferably injection molded, however, any other molding techniques are also applicable. The body can also be molded with smooth surfaces, in which case the threads are cut in by a subsequent operation. Likewise, while the use of plastic is preferred for the body it is to be understood that various other plastic like materials may be used such as the siloxanes. Preferred plastics include polycarbonate, or any other plateable plastic material. The metal coating is any material which has a high thermal coefficient such that its resistance changes markedly with the change in its temperature. Typical of such conductive metal is nickel, iron, platinum, rhodium, a mixture of temperature of percent nickel and 10 percent iron, and other materials familiar to those skilled in the art. The device of the present invention is preferably used to measure the temperature of the human body as more fully described in the above-identified patent application. In this application the conductive metal coating is so selected that it has a high thermal coefficient within the temperature range of the body normally from about 94 F. to 106 F. When the device is to be used for other purposes such as to measure the temperature within an oven, obviously other metals having a high thermal coefficient within the operating range of the oven are used.

The conductive metal is preferably applied in an electroless plating bath. These baths and their composition are already familiar'to those skilled in the art and, hence, need not be more fully described herein. However, other coating techniques including electrolysis and sputtering may also be used.

Having fully described the invention it is intended that it be limited only by the lawful scope of the appended claims.

lclaim:

l. A thermistor comprising a plastic body member of a generally cylindrical configuration having an opening passing longitudinally therethrough, a plurality of threads on the exterior of'said body in proximity to one end thereof, a thin metal film within the grooves but not on the lands of said threads and metal disposed on the exterior and interior of said body to establish a continuous metal path from the exterior of the end opposite said end having threads to the interior of said end opposite said end having threads, said metal path being composed of an electrically conductive metal having a high temperature coefficient of resistivity.

2. A thermistor comprising a plastic body member of a generally cylindrical configuration having an opening passing longitudinally therethrough, a plurality of threads on the exterior of said body in proximity to one end thereof, a thin metal film within the grooves but not on the lands of said threads and metal disposed on the exterior and interior os said body to establish a continuous metal path from the exterior of the end opposite said end having threads to the interior of said end opposite said end having threads, said metal path being composed of an electrically conductive metal having a high temperature coefficient of resistivity within the temperature range encountered in the human body.

3. A thermistor comprising a plastic body member of generally cylindrical configuration having a cylindrical opening passing longitudinally therethrough, a plurality of threads on the exterior of said body in proximity to one end thereof, a thin metal film within the grooves but not on the lands of said threads and metal disposed on the exterior and interior of said body to establish a continuous metal path form the exterior of the end opposite said end having threads to the interior of said end opposite said end having threads, said metal path being composed of an electrically conductive metalhaving a high temperature coefficient of restitivity within the temperature range encountered in the human body.

4. The method of making a thermistor which comprises molding a plastic body member having a generally cylindrical grooves of said threads to establish a continuous metal path from the exterior of the end opposite said end having threads to the interior of said end opposite said end having threads.

5. The method of claim 4 wherein the thermistor is subsequently coated with a thin protective coating.

. i i i i i 

1. A thermistor comprising a plastic body member of a generally cylindrical configuration having an opening passing longitudinally therethrough, a plurality of threads on the exterior of said body in proximity to one end thereof, a thin metal film within the grooves but not on the lands of said threads and metal disposed on the exterior and interior of said body to establish a continuous metal path from the exterior of the end opposite said end having threads to the interior of said end opposite said end having threads, said metal path being composed of an electrically conductive metal having a high temperature coefficient of resistivity.
 2. A thermistor comprising a plastic body member of a generally cylindrical configuration having an opening passing longitudinally therethrough, a plurality of threads on the exterior of said body in proximity to one end thereof, a thin metal film within the grooves but noT on the lands of said threads and metal disposed on the exterior and interior os said body to establish a continuous metal path from the exterior of the end opposite said end having threads to the interior of said end opposite said end having threads, said metal path being composed of an electrically conductive metal having a high temperature coefficient of resistivity within the temperature range encountered in the human body.
 3. A thermistor comprising a plastic body member of generally cylindrical configuration having a cylindrical opening passing longitudinally therethrough, a plurality of threads on the exterior of said body in proximity to one end thereof, a thin metal film within the grooves but not on the lands of said threads and metal disposed on the exterior and interior of said body to establish a continuous metal path form the exterior of the end opposite said end having threads to the interior of said end opposite said end having threads, said metal path being composed of an electrically conductive metal having a high temperature coefficient of restitivity within the temperature range encountered in the human body.
 4. The method of making a thermistor which comprises molding a plastic body member having a generally cylindrical configuration having an opening passing longitudinally there through and a plurality of threads on the exterior of said body in proximity to one end thereof, coating the inside and outside surface of said body with a thin electrically conductive metal film having a high temperature coefficient of resistivity, and removing said film from the lands of said threads but not the grooves of said threads to establish a continuous metal path from the exterior of the end opposite said end having threads to the interior of said end opposite said end having threads.
 5. The method of claim 4 wherein the thermistor is subsequently coated with a thin protective coating. 